1. Field of the Invention
Embodiments of the present disclosure are directed toward coiled tubes and methods of heat treating coiled tubes. Embodiments also relate to coiled tubes with tailored or varied properties along the length of the coiled tube.
2. Description of the Related Art
A coiled tube is a continuous length of tube coiled onto a spool, which is later uncoiled while entering service such as within a wellbore. Coiled tubes may be made from a variety of steels such as stainless steel or carbon steel. Coiled tubes can, for example, have an outer diameter between about 1 inch and about 5 inches, a wall thickness between about 0.080 inches and about 0.300 inches, and lengths up to about 50,000 feet. For example, typical lengths are about 15,000 feet, but lengths can be between about 10,000 feet to about 40,000 feet.
Coiled tubes can be produced by joining flat metal strips to produce a continuous length of flat metal that can be fed into a forming and welding line (e.g., ERW, Laser or other) of a tube mill where the flat metal strips are welded along their lengths to produce a continuous length of tube that is coiled onto a spool after the pipe exits the welding line. In some cases, the strips of metal joined together have different thickness and the coiled tube produced under this condition is called “tapered coiled tube” and this continuous tube has varying internal diameter due to the varying wall thickness of the resulting tube.
Another alternative to produce coiled tubes includes continuous hot rolling of tubes of an outside diameter different than the final outside diameter (e.g., U.S. Pat. No. 6,527,056 B2 describes a method producing coiled tubing strings in which the outer diameter varies continuously or nearly continuously over a portion of the string's length, WO2006/078768 describes a method in which the tubing exiting the tube mill is introduced into a forging process that substantially reduces the deliberately oversized outer diameter of the coil tubing in process to the nominal or target outer diameter, and EP 0788850 describes an example of a steel pipe-reducing apparatus, the entirety of each of which is hereby incorporated by reference, describe such tubes).
These methods described above produce coiled tube having constant properties since the tube is produced with the same material moving continuously through the same process. Therefore, the final design of the produced tube (e.g., dimension and properties) is a compromise between all the tube requirements while in service.